The persistence of foam in various aqueous industrial operations can cause process inefficiency and, in some cases, an inferior final product. The pulp and paper industry experiences some of the most troublesome foam problems. Common incessant foaming occurs in pulp washing and screening and papermaking processes. Stable foam also often surfaces during effluent wastewater treatment. Entrained air tends to be a more serious type foam. The spherical entrained air bubbles are finely dispersed in the bulk solution. Small bubble volumes tend to lack a sufficient buoyant force and thus often become attached to non-wettable fiber parts. These fibers and fines can flocculate to the surface and form dense stable foam. As a result, the stabilized bubbles can inhibit the drainage of washing liquor through the fiber mat which in turn slows down production. Entrained air is also known to impair paper formation and tensile strength.
Surface foam, on the other hand, is a more visible problem which can be evident in wire pits, stock chests and effluent ponds. The existence of surface foam surely indicates an entrained air problem. On the paper machine, collapsed surface foam can be carried back through the headbox and into the sheet where holes can be formed. On the deckers, mat filtration can be reduced when surface foam is picked up by the mat. Wastewater foaming can be hazardous to both the environment and man. In extreme cases, severe static foam can be blown across roads, thus creating traffic hazards and an unattractive mess.
Foam can be controlled by a variety of chemical methods. An effective antifoam should be slightly insoluble, yet dispersible, in the foaming medium. The antifoam should be able to control both entrained air and surface foam over a prolonged period of time. This present antifoam invention was developed to prevent or control the above described foaming problems while avoiding creating any undesirable side effects in the system or on the paper machines.